We have a 98 Grand Caravan SE 3.3L w/ 160K. It has run good for the 105K we’ve put on it, doesn’t consume oil or coolant. It had been knocking at highway speeds for a while, and developed a noticeable miss a month ago, and we took it in to our local guy - plugs were way overdue (85K!) according to the “severe service” intervals and he said “the plugs were fouled, but one was so bad, I can’t believe it was running”. So we did the plugs & wires, PCV, and an “induction system cleaning”. Better, but the miss was still there, so I immediately replaced the coil and tried to clean up the IAC, but ended up taking the van back to have the whole throttle body removed and cleaned. The miss is a little better but still there. It is most noticeable at or near idle when in gear, especially coming to a stop - it feels like it’s trying to lurch forward at engine speed, once per rev. It seems a touch better warmed up vs. cold. Out of gear at idle, it’s better, but I can still feel it.
Before the repairs, it was so bad that the idle speed would drop and it felt like it was close to stalling; now, at least the idle holds steady but the sensation of a torque pulsation is still there. Almost like one cylinder is way down on power.
The shop says that’s the way it’s going to be with an old motor, they noticed lots of blow-by when they “smoked” the motor, blah blah blah. I haven’t noticed lots of oil or coolant consumption or loss of power; it actually runs quite nice once we’re moving, now that it has working spark plugs again.
So I am skeptical of the explanation I got. I would like to fix it and keep the car for at least a few more years, but I got the feeling my current shop is not interested. There are no OBD fault codes to chase after, so what diagnostic steps should I be looking for a new shop to do?
Thanks for any advice - Dave
The next step is a compression test.
You may have a stuck/dirty injector. Sounds like a good time to try a can of Seafoam:
http://video.google.com/videoplay?docid=6187290865726229173#
Yes, a compression test is in order. That plug with excessive fouling may indicate an internal problem. But a miss fire from low compression should set a code. If the compression is not a problem a close look at all the sensor inputs might be enlightening. Intake air temperature, throttle position, manifold pressure, etc. could have a glitch that leans the fuel enough to cause the engine to stall but not set a code.
Thanks for the advice. I have a scanner w/ live data, but other than the scanner telling me there’s a problem (or an obviously bogus signal), I don’t know exactly what to expect for all the sensors that contribute to A/F ratio and spark advance. It has never actually stalled, but it has felt like it was missing a cylinder. When I had the mechanic just sit in driver’s seat for a minute the other day just to feel what I feel, he said it would be A LOT worse if it was truly only running on 5, so perhaps it’s one cylinder that’s just a little off. I have not seen any codes yet.
Any idea if the compression check can be done in place? The rear bank is not easy to get to; I’m wondering if I’d have to pull the upper intake to get to them. And if I do that, are there any checks I can do to the injectors while I’m in there, or is it just easier to replace them considering their age?
If the plugs can be replaced with the intake in place testing compression should not be a problem. If you watch live data while someone else drives you might see one of the inputs becoming somewhat erratic. Temperature should remains somewhat constant after the engine is fully warmed up. Look for changes in the data. What type scanner do you have? And as helpful as scanners are often it is necessary to back probe sensors to get a handle on minor glitches that can be major problems.
The back plugs are a bear to replace on the rear bank, the catalytic converter has to be removed to replace the passenger side one.
I guess I’ll have to try it to see - I just recall having to thread the tester in by twisting the hose was not easy, and it sounds like top-side access to the rear bank is not possible without taking something off (upper intake, wipers and cowl, alternator and bracket, etc.)
The scanner is the Actron 9580.
Now that I think about it, the “roughness” seems so strongly a once-per rev impulse, that it would seem to rule out a lot of sensor faults, unless there are some sensors that are on a per-cylinder basis. The usual “rough idle” suspects like inlet air temp, coolant temp, O2, TPS, inlet air control, vacuum leaks, etc. I would not expect to cause a once-per rev impulse that I feel through the steering wheel and driveline.
Would an individual bad injector or bad electrical connection to an injector show a code?
Could excessive compression (buildup) or lack thereof (leaks) in one cylinder be felt that strongly?
I see now why you said a compression check is the next step.
By the way, hilarious user name - that’s a candidate for the Car Talk end credits. Unless it’s actually your name, in which case I’m not laughing at all. Really.
The phrase I am most concerned with is “knocking at highway speeds for a while”. A miss is not at all important if your engine is knocking,could you clear this up?
About the “knocking” - maybe I should have said “pinging”. Anyway, for the last year or so, 55 on the highway was no problem, but at higher rpm (& load) like 65 or 70, I could hear a rattly sound from the engine that I could make go away if I backed off the gas pedal, or sometimes by stepping a little more on it, though it got to the point that nothing other than slowing down would get rid of it.
All that’s gone now since the new plugs and wires were put in, but this “miss” that developed only in the last month or so before the repair is still hanging around. It has changed a little as we made the successive repair attempts, so I suspect it might be related to cylinder fouling or a weak or dirty injector - something that may improve slowly over time as the engine recovers from the abuse we dished out by not taking care of the plugs sooner.
Also I’m going to throw a bottle or two of BG 44K or Techron at it to see if that makes a difference. It got a new fuel pump and filter a few months back, so it’s ready and rarin’ to go to ingest a tankful of crud from the extra detergent!
Running a compression test is always Step One when an engine performance problem exists. Always; and this means even on low miles engines.
The spark plugs were removed and one was apparently fouled so this engine was begging for a compression test. The plugs were out, kill that bird then and there.
The pinging could be due to one of several things; oil consumption in a cylinder (the fouled plug) and an EGR system fault. (clogged passages due to the oil consumption)
The spark plugs need to come back out and a compression test performed; something that should have been done on the first go around.
Compression check should tell you if you have a burnt exhaust valve. You might also want to look at the top of the intake valves when you remove the intake manifold. They are probably so full of deposits that you may want to scrape off with a screwdriver and a vacuum cleaner.
Sometimes the deposits fill the entire chamber and keep the valve from closing properly. The tapping could have been an important sign if you have rocker arms that could break. The intake valve will open a little without the rocker arm but it won’t open much. You are getting symptoms that could indicate mechanical troubles such as I described.
OBD, OBDAH, life goes on. OH-B-D-BA-OH-BA-DAH.
I can hardly believe it, but you were right (sorta).
I got home last night, told my wife about these conversations, and she says “When I drove it today and I hardly noticed it.” And I thought, “Oh great, an INTERMITTENT problem - now I’m really sunk.” So I started it up, and I could still feel it, but it was truly A LOT smoother. Hmmmmm.
So I pour in the can of Seafoam on top of the full tank, drive it around for 15 minutes to warm up the engine and tranny, do an infrared temp check on the 3 exhaust ports I can get to from the top, listen to the injectors with a stethoscope, everything seems fine but it’s still a little lumpy. Take it out on the highway for 10 minutes and give it a half-dozen really good WOT acceleration runs, and when I get off of the highway, the stumble is COMPLETELY GONE. And it stays gone for the rest of the 10 minute trip home.
I’m guessing the really bad fouling the mechanic saw on the plugs is finally cleaning itself out of the cylinders. I feel like I just dodged a bullet.
This is almost too good to be true…
I got home last night, told my wife about these conversations, and she says “When I drove it today and I hardly noticed it.” And I thought, “Oh great, an INTERMITTENT problem - now I’m really sunk.” So I started it up, and I could still feel it, but it was truly A LOT smoother. Hmmmmm.
So I pour in the can of Seafoam on top of the full tank, drive it around for 15 minutes to warm up the engine and tranny, do an infrared temp check on the 3 exhaust ports I can get to from the top, listen to the injectors with a stethoscope, everything seems fine but it’s still a little lumpy. Take it out on the highway for 10 minutes and give it a half-dozen really good WOT acceleration runs, and when I get off of the highway, the stumble is COMPLETELY GONE. And it stays gone for the rest of the 10 minute trip home.
I’m guessing the really bad fouling the mechanic saw on the plugs is finally cleaning itself out of the cylinders. I feel like I just dodged a bullet.
Driving it for only 30 minutes probably didn’t burn more than a gallon or so of gas, and thus only an ounce or two of Seafoam, so if the stumble comes back, you might try the “full” Seafoam treatment, which involves pouring some of it directly into the throttle body.
Yes, not much Seafoam really went thru in that short time, so I suspect the improvement has more to do with accumulating some run-time with proper combustion. But I will concede that the “magic potions” are probably helping to clean out the gunk.
I hope that the shop took care of the dirty throttle body when they ran the induction system cleaning the first time through, and then on a subsequent visit removed the throttle body for a thorough manual cleaning of the passages.
At this point, I am keeping my fingers crossed that the stumble does not come back, but I am hyper-aware of it now so I’ll be watching closely for recurring symptoms. I think a good long highway trip over the holiday (with a bottle of Techron on hand for the next tank) should prove it out one way or the other. And I still have the compression tester in the toolbox, though I really hope I don’t need to dust it off…
Thanks for your help!
For many years tuning up some cars included “blowing the soot out.” It might have been the most important part of the tune up on many of the cars which rarely saw even 50 mph and rarely even driven until fully warmed up. And, BTW, the infrared is a great way to find a miss fire. In my shade tree days I spit on the manifold.
I wouldn’t go dancing in the streets just yet OP; especially if this fouling is due to oil.
Happy to get a results posting. Hope the results stay good. I’m buying stock in the company that makes that Seafoam stuff. I used some last Summer and the truck is still running. 80,000 miles and still going!